The polymer clad quartz optical fiber has better light transmittance than the polymer core optical fiber. Further, it has a clad composed of an organic polymer and thus has better handling performance than glass clad optical fibers including better flexibility, allowing fabrication in larger diameters, and is therefore suitable for short or medium distance communications under severe environmental conditions as in factories.
For the composition of such polymer clad quartz optical fiber, a fiber having the core comprised of quartz glass and a clad comprised of a silicone resin is known.
However, for practical application, it is required to provide a cord structure with a covering layer disposed over the polymer clad quartz optical fiber in order to protect the clad quartz optical fiber from external excitation. For this reason a cord having a polymer clad quartz optical fiber, covered by a thermoplastic resin such as nylon resin, is known.
However, conventional polymer clad quartz optical fiber cords have had the shortcoming that, as the core was comprised of quartz glass while the clad and the protective or covering layer was formed of an organic polymer, these components had greatly different coefficients of thermal expansion. In a lower temperature region the organic polymer would shrink and the shrinking stress would apply a strain to the quartz to reduce the light transmittance of the optical fiber.
This shortcoming was particularly noticeable in a cord having a thermoplastic resin employed for the sake of economy or ease of control of covering thickness. When the cord structure was employed, the transmission loss at low temperature would increase more than that of the polymer clad quartz optical fiber comprised of only core and clad, precluding use of the thermoplastic resin under severe temperature conditions.
To solve this problem, the expedient of enlarging the inner diameter of the covering layer was proposed. However simply doing this causes an inferior relationship between the tension fibers and the optical fiber because of too loose packing of the tension fibers. Further, the optical fiber cord of this invention needs to easily be inserted in and connected with a connector, so its outer diameter must be determined relative to the inner diameter of the connector. Therefore, enlarging the inner diameter of the covering layer inevitably brings about too small thickness of the covering layer and causes insufficient protection by the covering layer.
An important object of the present invention is to provide a polymer clad quartz optical fiber cord which overcomes the problems just discussed. Another object is to provide a way of avoiding an increase of transmission loss of the polymer clad quartz optical fiber cord at lower temperatures. Still another object is to provide a cord which has a sufficient resisting force to drawing in wiring work and is thus distinguished in handling performance and workability, keeping its outer diameter at a known uniform and desired dimension so that it can be easily connected with an ordinary connector.
The foregoing and other objects of this invention, including the simplicity and economy of the same and the ease with which it may be applied to cords of different sizes, shapes and combinations, will further become apparent hereinafter in the drawings, of which:
The Figure is a cross-sectional view of a polymer clad quartz optical fiber cord comprising one embodiment according to this invention.